The present invention generally relates to communication systems, and, more particularly, to common public radio interface (CPRI) nodes in a communication system.
A communication system includes transmitter and receiver systems that exchange information with other communications systems in a communication network via optical fibers, electrical links, or wireless modes of communication. The communication systems that use a wireless mode of communication use radio-frequency (RF) signals, and hence, such communication systems are referred to as radio communication systems.
A radio communication system includes at least one radio equipment controller (REC) and one or multiple radio equipment (RE) nodes that exchange control signals through a common public radio interface (CPRI) link. The CPRI link includes at least one of an electrical and optical interface. The control signals thus exchanged follow a CPRI protocol such as an L1 in-band protocol. The CPRI protocol enables transmission of real-time baseband and input data as well as control information. Thus, the communication system is a real-time communication system. The control signals include link status signals such as loss of signal (LOS), loss of frame (LOF), and other layer 1 (L1) alarms such as remote alarm indication (RAI) and serial data interface (SDI).
Further, the RECs and the RE nodes are connected as communication nodes in a network topology. The network topology can be any one of star, tree, mesh, daisy-chain, bus, and ring topologies. Multiple RE nodes may be connected to one REC, multiple RECs may be connected to one RE node, and multiple RECs may be connected to multiple RE nodes based on the topology. The REC includes a baseband processor that decodes and encodes data traffic that is received and sent, respectively, by way of an antenna. The RE node includes a digital signal conditioning circuit for receiving the control signal from the REC by way of the CPRI link. The digital signal conditioning circuit modulates the strength of the control signal.
For example, the network topology may be a daisy-chain network topology and the communication system includes first through third radio equipment nodes. The REC is a master controller and the RE nodes are connected through the CPRI link such that a CPRI port of the REC is connected to a CPRI slave port of the first RE node. A CPRI master port of the first RE node is connected to a CPRI slave port of the second RE node. Similarly, a CPRI master port of the second RE node is connected to a CPRI slave port of the third RE node. Thus, the CPRI master port and the CPRI slave port of each RE node are connected to the CPRI slave port and the CPRI master port of adjacent REC or RE nodes, respectively. Further, each RE node includes a CPRI sub-system for configuring and maintaining the CPRI link and a processor.
When the REC sends a control signal through the CPRI link, the RE nodes connected in the daisy-chain network topology receive the control signal through the corresponding CPRI slave ports. A RE node may become unresponsive, i.e., does not respond to the control signal sent by the REC when at least one or a combination of the following scenarios occur—the processor of the RE node is in a hung state, electronic circuits on a system-on-chip (SoC) connected to the processor of the RE node malfunction, or when the CPRI sub-system behaves abnormally. Thus, the CPRI link may breakdown, thereby disrupting the daisy-chain network topology.
A known technique to eliminate the above-mentioned problem includes utilization of downlink (DL) and uplink (UL) function units and a reset function unit in each RE node. In one embodiment, the RE nodes and the REC are connected in a daisy-chain network topology and exchange control words by way of the CPRI link. When the processor of the second RE node is functioning abnormally, a DL function unit of the second RE node sets a software alarm notification field corresponding to the second RE node in the control words to 1 for indicating abnormality in the working of the second RE node. When the REC receives the control words, the REC identifies abnormality in the working of the second RE node based on the software alarm notification field corresponding to the second RE node. The REC sets a software reset field, in the control words, corresponding to the second RE node to 1 for resetting the second RE node. The REC transmits the control words and each RE node receives and decodes the control words to determine whether corresponding software reset field is set to 1 by the REC.
When the DL function unit of the second RE node identifies that the software reset field corresponding to the second RE node is set to 1, the DL function unit of the second RE node generates an output signal for the reset function unit of the second RE node. The reset function unit of the second RE node generates a reset signal to reset the second RE node based on the output signal. Subsequent to resetting of the second RE node, the UL function unit of the second RE node resets the software reset field corresponding to the second RE node to 0. The control words are transmitted to the REC, thereby indicating that the second RE node has been reset. Although the above technique resets a RE node, the technique does not provide a method for recovering the RE node without disrupting the network topology.
In another example, due to any malfunctioning of the processor and the SoC, the REC resets a RE node even though the CPRI sub-system that services the CPRI link is functional. Further, since the unresponsive RE node is the intermediate RE node, all RE nodes beyond the intermediate RE node require auto-negotiating operation for re-establishing the CPRI link. This causes large power and time overheads and creates chaos in the real-time communication system.
Therefore, it would be advantageous to have a system and method for recovering unresponsive common public radio interface (CPRI) nodes in a communication system, prevents disruption of network topology of the communication system, reduces time and power over head, and provides a recovery scheme for the unresponsive CPRI nodes in a phased manner.